<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>P72 【例4-1】demo01.html</title>
</head>

<body>
    <button id="btn">点击</button>
    <div id="demo" style="display:none">这是一个惊喜！</div>
    <script>
        function $(id) {
            return document.getElementById(id);
        }
        function show() {
            $('demo').style.display = 'block';
        }
        $('btn').onclick = show;
    </script>
    <a href="../首页/page04.html">
        <h2>返回上一页面</h2>
    </a>
</body>

</html>